1. Field of the Invention
This invention relates to a mobile communication terminal, such as a mobile phone or a PDA (Personal Digital Assistant), and a control data changing method thereof.
2. Description of the Related Art
Generally, the control memory of a mobile communication terminal stores an Authentication Key (A-Key) necessary for authentication in establishing communication, Number Assignment Module (NAM) Programming (hereinafter, abbreviated as NAM Pro), and a control data group set by the NAM Pro. The control data group is required for the carrier to manage the operation of mobile communication terminals suitably. Therefore, if a user changes the control data group arbitrarily after starting to use the mobile communication terminal, the carrier cannot guarantee proper service.
To overcome this problem, a conventional mobile communication terminal applies a guard called “Subsidy Lock” to the control data group, thereby preventing the control data group from being changed easily. The Subsidy Lock is set and released by a guard control code called a “Subsidy Lock Code.” A highly secure code, such as SPC, is used as the “Subsidy Lock Code.”
When a user purchases a mobile communication terminal, the salesclerk or user himself or herself registers control data, including the phone number allocated by the carrier to which the user subscribes, in the control memory of the mobile communication terminal. To register the control data, it is necessary to temporarily release the Subsidy Lock on the control data group already registered in the terminal. However, releasing the Subsidy Lock introduces the danger that other control data groups registered will be changed by the user accidentally or intentionally.
To avoid this problem, for example, the NAM Pro is provided with Simple NAM Programming (hereinafter, abbreviated as Simple NAM Pro) for changing only part of the control data, such as the phone number or the system ID. Then, when the phone number or the like is registered, only the Simple NAM Pro is started up. If the Simple NAM Pro is caused to remain running, there is a possibility that the user of the terminal will change the phone number or the like. For this reason, a guard called “One-Time Subsidy Lock” is applied to the Simple NAM Pro, too. The guard of the One-Time Subsidy Lock is released by a guard control code called “One-Time Subsidy Lock Code” only when the phone number is registered at the time of purchase of the terminal.
However, in the case where just inputting the One-Time Subsidy Code to the terminal enables the One-Time Subsidy Lock to be released, if a person knows only the One-Time Subsidy Code, he or she can unlock the guard relatively easily. Therefore, it has not been safe to say that the guard function for the Simple NAM Pro and the control data group set by the Simple NAN Pro is sufficient.